Final answer:
Calf diphtheria is primarily caused by Corynebacterium diphtheriae which releases a toxin leading to the formation of a pseudomembrane and can cause serious health issues.
Step-by-step explanation:
The primary organism that causes calf diphtheria is Corynebacterium diphtheriae, a gram-positive rod-shaped bacterium. This organism can become pathogenic and cause disease due to the diphtheria toxin, which is encoded by a temperate bacteriophage. The diphtheria toxin inhibits protein synthesis within the host's cells, leading to cell death. The accumulation of dead cells and other components such as pus and red blood cells can create a pseudomembrane across mucous membranes, a hallmark of the disease, and can result in serious complications such as obstruction of the pharynx or trachea, myocarditis, or nerve impairment.